1. Field of the Invention
The present invention relates to method for measuring defects in a transparent substrate, and more particularly a method for measuring inclusion and surface defects in the substrate.
2. Technical Background
The growing displacement of cathode ray tubes by flat panels as display devices for computers, televisions, personal digital assistants (PDAs) and cell phones, to name a few, has been nothing short of phenomenal. One principal component to flat panel displays, such as liquid crystal displays (LCDs), is the glass substrate between which the liquid crystal material is sandwiched. Such glass substrates must be pristine in nature, with no visible defects which may be easily discernable by the viewer. Often, multiple display devices are formed on a single substrate, after which the individual displays are cut from the substrate. Thus, glass substrate sheets must be rigorously inspected prior to their use in the manufacture of the display to reduce costs associated with unacceptable substrates.
A traditional inspection system for detecting defects or flaws in a transparent substrate includes an operator who uses one or more light sources to illuminate a substrate at various angles and, based on years of experience, make a determination as to the size and location of defects within the substrate. Often the defects are compared against limit samples to determine whether or not the substrate passes or fails. Defects are then categorized according to the intensity of the light source necessary for detection of the defect. For example, a 20,000 Lux defect is smaller (or fainter) than a 10,000 Lux defect, thereby requiring a higher intensity illumination for detection. Obviously, such a subjective approach to product quality is less than desirable in a modern manufacturing operation.